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            <h2 class="title" style="clear: both"><a id="reversesplit"></a>Reverse BTree Splits</h2>
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      <p>
            If your application is using the Btree access method, and your
            application is repeatedly deleting then adding records to your
            database, then you might be able to reduce lock contention by
            turning off reverse Btree splits.
        </p>
      <p>
            As pages are emptied in a database, DB attempts to
            delete empty pages in order to keep
            the database as small as possible and minimize search time.
            Moreover, when a page in the database fills
            up, DB, of course, adds additional pages 
            to make room for more data.
        </p>
      <p>
            Adding and deleting pages in the database requires that the
            writing thread lock the parent page. Consequently, as the
            number of pages in your database diminishes, your application
            will see increasingly more lock contention; the maximum level
            of concurrency in a database of two pages is far smaller than
            that in a database of 100 pages, because there are fewer pages
            that can be locked.
        </p>
      <p>
            Therefore, if you prevent the database from being reduced to a
            minimum number of pages, you can improve your application's
            concurrency throughput. Note, however, that you should do so
            only if your application tends to delete and then add the same
            data. If this is not the case, then preventing reverse Btree 
            splits can harm your database search time.
        </p>
      <p>
            To turn off reverse Btree splits, 
                <span>
                    provide the
                    <code class="literal">DB_REVSPLITOFF</code> flag to the 
                        
                        <code class="methodname">Db::set_flags()</code>
                    method.
                </span>
                
        </p>
      <p>
            For example:
        </p>
      <pre class="programlisting">#include "db_cxx.h"

...

int main(void)
{
    u_int32_t env_flags = DB_CREATE     |  // If the environment does not
                                           // exist, create it.
                          DB_INIT_LOCK  |  // Initialize locking
                          DB_INIT_LOG   |  // Initialize locking
                          DB_INIT_MPOOL |  // Initialize the cache
                          DB_THREAD     |  // Free-thread the env handle
                          DB_INIT_TXN;     // Initialize transactions

    u_int32_t db_flags = DB_CREATE | DB_AUTO_COMMIT;
    Db *dbp = NULL;
    const char *file_name = "mydb.db";

    std::string envHome("/export1/testEnv");
    DbEnv myEnv(0);

    try {

        myEnv.open(envHome.c_str(), env_flags, 0);
        dbp = new Db(&amp;myEnv, 0);

        // Turn off BTree reverse split.
        dbp=&gt;set_flags(DB_REVSPLITOFF);

        dbp-&gt;open(dbp,        // Pointer to the database 
                  NULL,       // Txn pointer 
                  file_name,  // File name 
                  NULL,       // Logical db name 
                  DB_BTREE,   // Database type (using btree)
                  db_flags,   // Open flags 
                  0);         // File mode. Using defaults

    } catch(DbException &amp;e) {
        std::cerr &lt;&lt; "Error opening database and environment: "
                  &lt;&lt; file_name &lt;&lt; ", " &lt;&lt; envHome &lt;&lt; std::endl;
        std::cerr &lt;&lt; e.what() &lt;&lt; std::endl;
    }

    try {
        dbp-&gt;close(dbp, 0);
        myEnv.close(0);
    } catch(DbException &amp;e) {
        std::cerr &lt;&lt; "Error closing database and environment: "
                  &lt;&lt; file_name &lt;&lt; ", " &lt;&lt; envHome &lt;&lt; std::endl;
        std::cerr &lt;&lt; e.what() &lt;&lt; std::endl;
        return (EXIT_FAILURE);
    }

    return (EXIT_SUCCESS);
} </pre>
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